Able to Add, but Unable to Remove Mapped Domain

Hello,

I am trying to update our WPMU site with some new domains for mapping. I was able to map a new domain by the Site ID. But I am unable to find where to remove the existing URL mapped for the same Site ID.

From Dashboard > Settings > Domains - I see a few, but it definitely doesn't look like all of them. This is where I added a new URL for Site ID 40. But I am unable to find and remove "homeresource1.com" to leave "homeresourcenc.com" as the only mapped domain for Site ID 40.

I also noticed in WPMU Dev > Plugins - Domain mapping is not installed, however; I do see it from my Dashboard. This makes me suspect something is awry with the plugin installation.

Is it possible part of the plugin/configuration is missing? Or do I need to remove the domain mapping elsewhere?

Thank you in advance for your assistance in this matter.